A track/hold circuit is an important component of a high speed Analog-to-Digital Converter (ADC) which requires high speed accurate sampling of an analog signal. Typically to achieve 12 bit accuracy, the aperture jitter must be less than 0.01 nanoseconds for a 10 MHz signal sampled to an accuracy less than 1 millivolt. For a 10 bit video signal, the aperture jitter must be less than 0.06 nanoseconds. It is difficult to achieve such timing accuracy independent of the voltage level of the input signal which can vary in amplitude a few volts using the well know CMOS transmission gate (the parallel combination of an n-channel and a p-channel MOS transistor) as a sampling element. This transmission gate is not well suited for precise timing accuracy since the rise and fall time of the clock signals used to control same are typically in the order of 0.5 to 1.5 nanoseconds and their gradual shutoff characteristic could easily result in wide variation of the effective sampling time period as the input signal varies over the full scale range.
The fastest known commercially available track/hold circuits are hybrid-bipolar combinations which can not be commercially formed on a CMOS integrated circuit chip. In addition, these combinations are not as fast as may be required in very fast ADC's.
It is desirable to have a high speed ADC which uses only CMOS compatible components that can be fabricated on a Silicon-On-Sapphire (SOS) integrated circuit chip or on a conventional integrated circuit chip.